1. Field of the Invention
The present invention relates to the fabrication of foam gaskets. More particularly, this invention relates to a method for fabricating gaskets from foamable organosiloxane compositions. The gaskets can be used on the sealing surfaces of automobile parts and electric/electronic components.
2. Background Information
Organosiloxane compositions that foam while curing, hereinafter referred to as foamable organosiloxane compositions, are well known and are used, for example, as sealants for perforated parts in nuclear power stations. Because of its limited storage stability under ambient conditions this type of foamable organosiloxane composition is generally Stored in two parts as two parts, typically referred to as base and curing agent, and a foam is produced by mixing the two parts, thereby initiating the simultaneous foaming and curing reactions.
Foam gaskets prepared from foamable, curable organosiloxane compositions have recently begun to be used at the seal regions of various types of objects such as automobile headlights, lids and covers for various types of containers, and waterproof casings for automotive electronic components. These end use applications are described in Japanese Laid Open Patent Application [Kokai or Unexamined]Number Hei 3-94876 [94,876/1991 ]). A disadvantage of the fabrication method described in this patent publication is that when the two liquid parts of a foamable organosiloxane composition are mixed in an enclosed system, a foam gasket having the desired uniform, small cells is not always obtained. In particular, foam having nonuniform cells is the only product obtained using high-viscosity foamable organosiloxane compositions.
Injecting a compressed inert gas such as air into a foamable, curable organosiloxane compositions to stabilize the cell structure of the resultant foam is described in commonly assigned U.S. Pat. No. 5,175,171, however no criticality with respect to the amount of air injected based on the amount of foamable composition is disclosed.
When a foamable organosiloxane compositions is used to fabricate foam gaskets, it is first extruded into a bead after mixing in a mixer, and after extrusion it must maintain this bead shape until foaming has begun. The maintenance of a high viscosity is therefore required, with the result that a foam gasket having uniform cells cannot be obtained.
An objective of the present invention is to provide a stable, method for fabricating large quantities of foam gaskets with uniformly small cells.